What color was the velour fabric?
It could be disintegrating foam but if the foam still feels soft and squishy, then that is not so likely. Latex foam that is 25++ years old will dry out and crumble into a very fine dust but it's more the color of ground mustard seeds, less like paprika. And you'd have noticed that it feels hard before you had the issue with the chocolate milk.
Urethane foam is way more common in that era of furniture than latex was, and it will break down too but usually it's a dirty brownish color and the crumbs are annoyingly clingy when you try to brush them away.
Do you know where the foam was manufactuered? If there's one of those big white tag labels with upholstery information on it somewhere, it will have the information. Some countries have different recipes for foam.
I wouldn't worry too much about toxicity. I believe foam is most toxic when it burns. I don't think it degrades into particles fine enough to be airborne, or at least not airborne for long. (If you ever have to scrape crunchy dry latex foam off of a furniture frame, it's probably a good idea to wear a particle mask, otherwise just be reasonably careful---sweep it up, vacuum, don't use it to season goulash or potato salad.)
I have not had goulash in a decade...and it sounds good right now. As for the base foam crumble, the fabric ( as noted) is attached to the foam covered frame with velcro....there are no staples. Consider having your upholster remove the velcro'd cover...and replace the crumbling problem...then re-attach the cover. Just don't give up on them...especially the sofa's. Destined to be a classic.
Yup,
Aunt Mark
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